1. Field of the Invention
The present invention relates to a piezoelectric fan that discharges warm air between heat dissipating fins of a heat sink, and a cooling device that includes such a piezoelectric fan.
2. Description of the Related Art
For recent electronic devices, countermeasures against heat inside the devices are becoming more important as the size of the device main body is further reduced and the high-density mounting of components progresses. For example, in personal computers, in addition to the size of device main body being reduced, the speed of CPUs is increasing in order to improve information processing performance. Therefore, while the high-density mounting of components leads to reduced ventilation inside the electronic devices, the amount of heat generated by the CPUs is increased. In such an environment, it is important to discharge warm air between heat dissipating fins of a heat sink disposed on the upper surface of a CPU and to thereby prevent an increase in the temperature of the CPU.
A piezoelectric fan that discharges warm air between heat dissipating fins of a heat sink is disclosed, for example, in KANEKO, “Shindo-shite kaze wo okuru hito-shinku wo jitsuen-tenji,” (online), Sep. 25, 2009, Nikkei WinPC, (searched Oct. 16, 2009), Internet (URL: http://pc.nikkeibp.co.jp/article/news/20090925/1018872/?f=news) (hereinafter referred to as KANEKO). The structure of the piezoelectric fan shown in KANEKO and a cooling device including the piezoelectric fan will be described with reference to FIGS. 1 to 3.
FIG. 1 is a perspective view showing the configuration of the piezoelectric fan of KANEKO. FIGS. 2 and 3 are perspective views showing the configuration of a cooling device including the piezoelectric fan of KANEKO. A piezoelectric fan 10 includes a vibrating plate 11, piezoelectric elements 12, and a supporting plate 13. A heat sink 20 includes a plurality of heat dissipating fins 22 extending from a base portion 21 upward and parallel or substantially parallel to each other. In FIGS. 2 and 3, a heat generating body 50, such as a CPU, is mounted on a circuit board, and the bottom surface of the heat sink 20 is disposed on the upper surface of the heat generating body 50 so as to be thermally coupled thereto. A cooling device 1 is configured by fixing the piezoelectric fan 10 to the heat sink 20, which is made of aluminum.
The piezoelectric elements 12 are each made by forming electrodes on both surfaces of a piezoelectric ceramics and polarizing the piezoelectric ceramics. The piezoelectric elements 12 are each a vibrating body that expands and contracts in response to the application of a voltage.
The piezoelectric elements 12 are attached to both surfaces of the vibrating plate 11. By expanding and contracting the piezoelectric elements 12, the vibrating plate 11 is bent. A plurality of blades 14 are provided in front of a portion of the vibrating plate 11 to which the piezoelectric elements 12 are attached. The blades 14 swing in response to bending of the vibrating plate 11.
A back end portion of the vibrating plate 11 located behind the portion to which the piezoelectric elements 12 are attached is fixed with screws 15 to the upper portion of the heat sink 20 with the supporting plate 13 disposed therebetween such that the plurality of blades 14 are located in the grooves between the heat dissipating fins 22 of the heat sink 20.
With this configuration, heat generated in the heat generating body 50 is conducted to the heat sink 20, air is warmed by the heat dissipating fins 22, and warm air is generated between the heat dissipating fins 22. The piezoelectric fan 10 discharges the warm air between the heat dissipating fins 22 by swinging the plurality of blades 14.
However, in the piezoelectric fan 10 of KANEKO, the heat dissipating fins 22 are covered by the vibrating plate 11, and therefore, the ventilation of the grooves between the heat dissipating fins 22 is reduced. In addition, in the piezoelectric fan 10 of KANEKO, the amount of bending displacement of the vibrating plate 11 to the applied voltage is relatively small, and vibration transmitted to the blades 14 is relatively weak. Therefore, the amplitude of the blades 14 is relatively small, and the airflow generating capability is relatively low.
When the piezoelectric fan 10 of KANEKO is installed on the heat sink 20, it does not have much of an effect on the heat dissipation from the heat dissipating fins 22. In recent years, many fast CPUs that generate a large amount of heat have been produced. Unfortunately, the piezoelectric fan 10 of KANEKO cannot sufficiently cool such CPUs.